The long-range objectives of the Colorado Learning Disabilities Research Center are the identification, characterization, validation and amelioration of etiologically distinct subtypes of dimensions of learning disabilities. To accomplish these objectives, test batteries that include psychometric measures of cognitive and academic abilities (Research Project I),, reading, language and perceptual processes (Research Project II), and ADHD and executive functions (Research Project III) will be administered to a sample of 50 pairs of identical twins and their sibling and 50 pairs of fraternal twins (both same-sex and opposite-sex) and their siblings, in which at least one member of each twin pair is reading disabled, to an independent sample of 50 pairs of identical twins and 50 pairs of fraternal twins and their siblings, in which at least one member of each twin pair has ADHD, and to a comparison group of 50 pairs of identical twins and 50 pairs of fraternal twins and their siblings, with no school history of learning disabilities or ADHD. Resulting data will be used to assess the genetic and environmental etiologies of reading deficits, ADHD and their co-morbidity, as well as their co-variation with measures of phonological and orthographic coding, reading comprehension, mathematics performance, and executive functions. In order to map quantitative trait loci that influence learning disabilities, and conduct association and mutation analyses, blood samples will be obtained from families of all twin pairs (Research Project IV). Concurrently, a longitudinal study of 340 pairs of identical and fraternal twin pairs will be conducted beginning at four years of age and continuing through second game Measures for the preschool children will include a dynamic assessment of their ability to learn sensitivity to phonomes, as well as other pre-reading, reading, attention and language skills (Research Project V). An administrative core unit will be responsible for coordinating the activities of the five research projects, maintaining communication among the participating investigators; ascertaining and scheduling subjects; obtaining questionnaire data and blood samples from families of twins; and administering the Center budget and other fiscal matters.